The image forming apparatus for forming an image onto the transfer sheet by using an electro photographic system or an inkjet system has become popular. In many cases, this image forming apparatus includes two kinds of mode. The first mode is a mode for printing an image onto an image area 32 of a transfer sheet 31 leaving a margin area 33 on a circumference thereof, (which will be called a normal mode) as illustrated in FIG. 12(a). The second mode is a mode for printing an image onto a full surface of the transfer sheet without leaving a margin area on a circumference thereof as illustrated in FIG. 12(b), (which will be called a full surface image mode).
Here, in the full surface image mode, there is a problem that in order to print an image even on the edge section of the transfer sheet, each section of the image forming apparatus gets dirt due to the toner image positioned outside the transfer sheet and the dirt gets into the edge portion and the rear surface of the transfer sheet. Thus, in order to remove this dirt, cleaning devices are provide in respective sections of the image forming apparatus and the cleaning devices conduct cleaning processes after completing the printing of the image onto the transfer sheet and before conducting the printing operation of the next transfer sheet.
With respect to the cleaning process in the full surface image mode as described above, for example, Japanese Patent Application Publication No. 2001-117382 discloses a method of executing a cleaning operation of a transfer roller, which is conducted in a post-rotation process, when finishing the image forming process conducted after completing the fixing operation, for a longer time than that in a normal print mode, in a full surface print mode of the image forming apparatus having two modes including a normal print mode where a print impossible area is provided on the circumference portion and a full surface area print mode where an image can be printed onto the full surface area of the transfer sheet without proving the print impossible area in the circumference portion of the transfer sheet. Even though the toner dirt occurs with a transfer roller, the dirt can be removed and a fine image is obtained on the full surface of the transfer sheet.
However, in order not to adhere the dirt onto the next transfer sheet, the cleaning process has to be completed before conducting the print operation of the next transfer sheet. As a result, as illustrated in FIG. 12(b), it is necessary to secure a long interval to the next transfer sheet. Thus, in the full surface image mode, there was a problem that the output productivity was extremely lowered.
A main object of the present invention is to provide an image forming apparatus and a control method, which are capable of suppressing the lowering of the output productivity in the mode where an image is printed on the full surface of a transfer sheet to solve the problems described above.